"uname -s" extension for macosx

[GoogleCodeExporter]

Seems to compile and install on macosx (10.7.4) after installing the ports 
through macports. HOWEVER, the Makefile needs to include macosx detection, the 
result of "uname -s" is below:

% uname -s
Darwin

for reference, the ports are at least:

sudo port install gtkglextmm
sudo port install gtkglext
sudo port install glew

Original issue reported on code.google.com by bog...@sweetcaesar.com on 1 Aug 2012 at 5:20